Thermoformable conductive laminate and process

ABSTRACT

A process for making a thermoformable conductive plastic laminate for use in making plastic parts adapted for electrostatic spray painting of a uniform high quality paint finish includes forming a matte release coated casting sheet, casting an electrically conductive polymer in thin film form on the casting sheet, drying to form a conductive primer coat, and transfer-laminating the conductive coating to a thin, thermoformable plastic face sheet. The matte release coat has a fine particulate filler that transfers a micro-toughened matte surface to the conductive primer coat. The conductive primer includes a polyester resin containing a fine particulate conductive material such as carbon black and, preferably, an anti-blocking agent such as fumed silica. The primer coated face sheet can be thermoformed and bonded to a underlying plastic substrate panel. The conductive primer has sufficient elongation and maintains uniform electrical surface conductivity and film thickness throughout the transfer-laminating, thermoforming and substrate panel-cladding process. The uniform surface resistivity of the conductive primer film is sufficient to permit electrostatic spray painting of the finished contoured panel and in one embodiment produces a Class &#34;A&#34; quality exterior automotive paint finish on the resulting panel.

CROSS-REFERENCE TO RELATED APPLICATION

This is a division of application Ser. No. 08/316,818 filed Oct. 3, 1994now U.S. Pat. No. 5,490,893 which is a continuation of application Ser.No. 08/067,527, filed May 24, 1993, now abandoned, which is acontinuation-in-part of application Ser. No. 07/887,535, filed May 22,1992 now abandoned.

FIELD OF THE INVENTION

This invention relates to the use of a thermoformable conductivelaminate in the electrostatic painting of plastic substrate panels.

BACKGROUND OF THE INVENTION

One embodiment of the present invention relates generally to theelectrostatic painting of plastics. Although the invention is describedbelow with relation to the electrostatic spray painting of plastic carbody panels, it should be understood that the invention has further useswhich will become more apparent from the description to follow.

In a typical electrostatic spray painting process, the spray head ismaintained at a high voltage (50-140 KV) while the object being sprayed(the substrate) is electrically grounded. When a metal substrate ispainted, it is relatively simple to maintain the metal at groundpotential. In the electrostatic painting process, particles (paintdroplets) are charged by an electrode in the spray head, and a chargedspray cloud from the spray head is attracted to the metal surface by thehigh voltage difference. This process greatly reduces over-spray andproduces a high quality surface on the painted metal parts. For thesereasons, and others, electrostatic spray painting techniques have beenused for many years in the automotive industry for spray paintingexterior body panels made of sheet metal.

In recent years, the automotive industry has increased its use ofplastic materials for exterior car body panels and trim parts. Thepredominant reasons are weight-reduction and the fact that car buildershave had available more sophisticated high impact strength plastics suchas polycarbonates. To a large extent, the future success of plastics forlarge car body panels will depend on their ability to be painted"on-line" in the assembly plant with a class "A" quality appearancesimilar to painted metal car body panels. Electrostatic spray paintingof plastic car body panels has been used for years. However,difficulties arise when using electrostatic spray techniques forpainting plastic substrates. The problem is particularly difficult whenthe objective is to paint plastics with the same high quality andappearance as metal parts using electrostatic paint spray equipment.

In order to electrostatically spray paint plastic substrates, a numberof technical problems must be overcome. For instance, electrostaticcharges accumulate on the surface of a plastic substrate during theelectrostatic spray painting process. The charges that accumulate do notdissipate as readily as with metals. This accumulation of chargesreduces the potential between the spray head and the substrate, leadingto weaker electrical forces on the charged paint droplets. Theaccumulated charges on the substrate surface also cause an opposingelectrical field that repels air-borne paint particles; and theaccumulated charges tend to produce a non-uniform field across thesurface. These phenomena produce a self-limiting effect of yielding lesspaint deposition and producing less uniformity in the build-up of thepaint film when compared with painting metal substrates.

In addition, some plastics have retained charges that may continue toexist for long time periods after the paint has been sprayed, making thepainted surface more vulnerable to dust attraction.

As a result of these problems, it has been difficult to achieve a highquality Class "A" paint coat by electrostatic painting of plastics. Theproblem is particularly difficult when the objective is to apply uniformpaint coats to plastic panels having complex three-dimensional shapes.

One solution to the problem has been to search for certain plasticsubstrate materials that will alleviate the surface charge problem andthe resulting low deposition and non-uniform build-up of paint films onplastics. This approach has not proved successful to date.

Another approach has been to develop electrically conductive primerswhich are air-sprayed onto the plastic substrate prior toelectrostatically spraying on the finished paint film. Use of aconductive primer can reduce the problems of accumulated electrostaticcharges, low paint film build-up and non-uniform conductivity and filmthickness. A further approach has been to add conductive materials tothe molding compound, but this can degrade the physical properties ofthe finished part. Use of conductive polymers has also been tried, butthis approach is too expensive.

In order to use such conductive primers, certain technical problemsfirst must be overcome. There is a need for good adhesion of the primerto the plastic substrate. Special problems have been controlling thesurface smoothness of the primer and achieving good adhesion to lowenergy substrates such as TPO (thermoplastic polyolefin) andpolypropylene. The conductive primer also should have a good level ofsurface conductivity along with humidity insensitivity, uniformity ofconductivity across the primer surface, and durability. If surfaceconductivity is too low, non-uniform build-up of the paint film canresult. Surface conductivity, as measured in terms of "resistivity"(ohms per inch or ohms per square), should be reasonably insensitive tohumidity; otherwise non-uniformities in conductivity and in the paintfilm build-up are produced. Other factors also can alter the uniformityof surface conductivity. When coating thickness varies as the primer isapplied, it is also more difficult to achieve such uniformity.

Generally speaking, the use of conductive primers for plastic substratepanels in the automotive industry has not been successful ineconomically producing a Class "A" quality finish. Because ofnon-uniform conductivity and primer film thickness, these primingtechniques have resulted in a generally poor appearance of the finishedpaint film. That is, a non-uniform primer, even though an undercoat inthe process, can create a poor appearance of the finished exterior paintcoat. It is difficult to produce a uniform paint film thickness with aprimer applied by non-electrostatic air spray techniques, followed byair spraying a charged-particle paint film. Moreover, even with uniformconductivity and primer thickness, the sprayed surface can result inless than a Class "A" finish, such as an "orange peel" surface. Inaddition, the techniques of using conductive primers have resulted in ahigh scrap rate and increased production time. The current method ofpriming plastic parts for electrostatic paint spraying is by adding anadditional step by either shipping to a separate location for priming,or priming on the paint line at the assembly plant. This amounts to hightransportation and handling costs and a higher than normal scrap returnrate. It also creates an additional source of volatile organiccompounds. If the full car body is successfully made of plastic, thecurrent use of a plating bath for metal parts can be eliminated from theproduction process.

The present invention, in one embodiment, provides a thermoformableconductive laminate that converts a non-conductive surface to aconductive surface for electrostatic painting applications. Theconductive laminate overcomes the problems of non-uniform conductivityand film thickness, as well as providing a high level of conductivityuniformly across the surface of the laminate. The laminate is formed bytechniques that provide a uniform conductive primer on the surface ofthe thermoformable laminate. The resulting laminate can be thermoformedinto complex three-dimensional shapes which can then beelectrostatically sprayed with a uniform paint coat after thermoforming.When used as a component in a plastic car body panel, the thermoformedlaminate can be bonded to a substrate, for example, molded withthermoplastic resins, or molded with thermoset resins by various sheetmolding techniques, or vacuum pressure formed and bonded to the plasticsubstrate. Examples of molding techniques and materials include SMC(sheet molding compound), BMC (bulk molding compound), TMC (thickmolding compound), RIM (reaction injection molding), and RTM (resintransfer molding). (TMC is a trademark of Takela Chemical Industries,Ltd.) The primed part is then ready for painting directly after moldingwith thermoplastics or thermosets, or vacuum pressure forming. Thiseliminates the extra transportation and cycle time costs associated withthe current off-line process of electrostatically spray painting plasticcar body panels.

As a further advantage, the conductive primer retains uniformity of itsconductivity throughout the thermoforming process. The primer comprisesan electrically conductive uniform film with good elongation andadhesion properties. By maintaining its uniform conductivity duringthermoforming, a paint coat applied to the primed conductive surface canachieve a Class "A" quality finish, even for complexly shaped panels.Less over-spray and scrap rate also are produced.

In addition to its use in the automotive industry, the invention can beused for making any contoured plastic panel in preparation forelectrostatic spray painting. The thermoformable conductive laminate canbe used for making doors or cabinets, or used in the electronicsindustry, for example, in electromagnetic shielding.

SUMMARY OF THE INVENTION

Briefly, one embodiment of this invention comprises a process for makinga thermoformable conductive plastic laminate that can be used to makeplastic parts adapted for electrostatic spraying or electromagneticshielding to produce a uniform painted finish. The process includesforming a temporary flexible casting sheet, preferably release coated,more preferably matte release coated, followed by casting onto thecasting sheet an electrically conductive polymeric material in thinliquid film form of uniform film thickness. The electrically conductivepolymeric material or primer, in one embodiment, includes a polyesterresin containing a fine particulate conductive material, such as carbonblack, and an anti-blocking agent, such as a dispersion of fumed silica.The components of the formulation are controlled so that upon drying toa uniform film thickness by solvent evaporation, the surface resistivity(or conductivity) of the conductive primer film is electrostaticallysprayable. A conductive primer coat which is electrostatically sprayableis in an optimal range of about 110 units or more on the Ransberg scale,or from about 5 to about 50 K-ohms/inch. The conductive primer hasinherent adhesion qualities to adhere to a plastic face sheet, and underthermolaminating techniques the primer is transferred from the castingsheet to a thin, semi-flexible, thermoformable plastic face sheet by drypaint transfer laminating techniques. The resulting laminate then can bethermoformed into a complex three-dimensional shape, such as the shapeof a car body panel. The carbon black and fumed silica contained in theprimer accelerate the solvent release and produce a smooth coating thatcan produce a Class "A" quality exterior automotive paint finish whensubsequently painted by electrostatic spray painting techniques. Thepreformed laminate can be bonded to an underlying plastic substratematerial by injection cladding or thermoset molding techniques, forexample, to form the finished article. The conductive primer coat hassufficient elongation and is able to maintain uniformity of conductivitythroughout the thermoforming process so that the high quality finishedpaint coat can be produced on the outer surface of the resultingsubstrate. The electrical surface resistivity is retained within itsdesired range throughout the transfer-laminating step and thethermoforming step.

As a further advantage, the invention is useful in the electrostaticspray-painting of high temperature-resistant plastic substrate panels.These panels are commonly made by the so-called engineering plasticsusing thermoset molding techniques. In some instances electrostaticspray painting of these plastics in the past has experienced adhesionproblems; however, the conductive primer of this invention provides goodadhesion, as well as good surface conductivity, for these substratepanels.

These and other aspects of the invention will be more fully understoodby referring to the following detailed description and the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating steps in a process for makingpanels from a thermoformable conductive laminate according to principlesof this invention.

FIG. 2 is a schematic cross-sectional view illustrating one embodimentof a matte release coated carrier and conductive primer coated laminateused in a process for making electrostatically sprayable plastic panels.

FIG. 3 is a schematic elevation view illustrating an in-line process forapplying the matte release coat and the conductive primer coat.

FIG. 4 is a schematic elevation view illustrating a transfer-laminatingstep of the process.

FIG. 5 is a schematic view illustrating a thermoforming step of theprocess in which a paint coated laminate is heated prior to vacuumforming.

FIG. 6 is a schematic view illustrating another thermoforming step inthe process.

FIG. 7 is a schematic cross-sectional view illustrating a preliminarystep in an injection-cladding step of the process.

FIG. 8 is a schematic cross-sectional view illustrating a substratematerial injection molded behind the thermoformed laminate in aninjection mold.

FIG. 9 is a schematic cross-sectional view illustrating a contouredplastic car body panel having an electrostatically spray paintedexterior weatherable Class "A" automotive paint finish.

FIG. 10 is a schematic side elevational view showing a process forforming a conductive composite laminate comprising a conductive coatingand an extruded plastic sheet.

FIG. 11 is a schematic side elevational view showing a process forforming a conductive laminate comprising a conductive coating and anextruded plastic sheet.

DETAILED DESCRIPTION

FIG. 1 is a schematic block diagram illustrating steps in a process forelectrostatically spray painting plastic panels made with athermoformable conductive laminate according to this invention. Theprocess is described in relation to its use in making exteriorautomotive body panels having an electrostatic spray painted finish,although other uses of the invention are possible as will become moreapparent from the description to follow.

Referring to FIG. 1, a paint coat with a surface capable of exteriorautomotive use is applied to a molded contoured plastic car body panelby electrostatic spray techniques. The process includes applying arelease coat 20 to a carrier sheet 22, followed by drying the releasecoat on the carrier. The preferred release coat is a matte release coatbecause of its processing advantages described below; however, otherrelease coats may be used. The process further includes applying anelectrically conductive resinous coating of uniform film thickness tothe release-coated carrier, and drying the conductive coating on thecarrier to form a uniform conductive primer coat 24. An optional sizecoat 25 is applied to the primer, followed by drying the size coat.There are several options in bonding the conductive primer coat to aplastic substrate panel. In one option, the conductive primer coat istransfer-laminated to a thin, thermoformable plastic face sheet 26. Thesize coat 25 bonds the conductive primer to the face sheet. The carrieris stripped away in the transfer-laminating step to release the carrierand its matte release coat from the primer. The matte release coatremains bonded to the carrier that is stripped away. The thermoformableconductive laminate can be bonded to an extruded plastic substrate panel28 and then thermoformed to a finished substrate in a subsequentthermoforming step 30; or the conductive laminate can be thermoformed ina thermoforming step 32 to form a thin, contoured, conductive facesheet, followed by bonding the conductive face sheet to a molded plasticsubstrate panel 34. The substrate panel can be formed by thermoset orthermoplastic molding, or vacuum pressure forming techniques. FIG. 2illustrates an extruded tri-layer substrate panel having mutually bondedextruded layers 28a, 28b and 28c described in more detail below. Anoptional size coat 27 can be coated on the face sheet 26 to improvebonding to the substrate. Referring again to FIG. 1, the conductiveprimer also can be laminated directly to an extruded face sheet, in anextrusion laminating step 35. In this option, the conductive face sheetthen can be thermoformed 32 and bonded to a molded substrate 34. Theconductive primed laminate can be shaped into the desired highlycontoured finished shape while maintaining a high level of conductivitysufficient for subsequent electrostatic spray coating of an exteriorautomotive paint film 36. The finished paint coat can be a weatherable,durable glossy exterior automotive paint. These include the more rigidhighly cross-linked thermoset enamel, urethane or acrylic lacquers, aswell as more flexible paint finishes of vinyl, or fluoropolymer resins.Of the latter type are polyvinylidene fluoride (PVDF) or PVDF-acrylicblends. The conductive primer retains uniformity of its conductivitythroughout the thermoforming and substrate molding steps and facilitatesforming a Class "A" exterior automotive finish electrostatically spraypainted on the contoured panel surface.

FIG. 2 schematically illustrates one embodiment of the process formaking the thermoformable laminate. The matte release coat 20 is coatedonto the surface of a flexible, foldable, heat resistant,self-supporting carrier sheet 22, also referred to in the art as acasting film. The carrier sheet is preferably a polyester casting filmsuch as Mylar (a trademark of Du Pont), or American Hoechst 2000 PETfilm. The polyester carrier film has a sufficiently high heat resistanceto resist axial elongation under temperatures applied during subsequentmatte release coat and primer coat drying steps.

The matte release coat 20 comprises a thermosetting resinous coatinghaving a low gloss matting agent dispersed in it, together with arelease agent which freely releases the release coated carrier fromcoatings applied subsequently to the carrier. Other release systems arepossible at a range of gloss levels. In one embodiment the release agentincludes a wax component contained in the synthetic resinous coating forenhancing release of the matte release layer, together with a siliconeresin component in the coating for further enhancing release properties.In a preferred embodiment, the wax component is a polyethylene wax. Thecoating 20 is preferably applied by gravure coating techniques and driedin air in a drying oven at approximately 220° to 250° F. to cross-linkthe resin and bond the release coat to the carrier. In some instances,such as dry paint transfer laminating steps in which the primer coat istransferred to a high temperature-resistant polymer sheet such aspolyarylate, the release coat (including its thermoset resin component)can be omitted.

The conductive primer coat 24 is then coated on the release coatedcarrier. The conductive primer preferably comprises a thermoplasticsynthetic resinous material containing a sub-micron size filler such ascarbon for providing electrically conductive particles uniformlydispersed throughout the resin. The preferred conductive filler iscarbon black. The conductive primer is a flexible synthetic resinous dryfilm-form coating having electrically conductive properties describedbelow. In some cases the conductive primer can comprise a lightlycross-linked thermosetting resin to increase the temperature resistanceof the primer coat. In either case, the resinous conductive coating isflexible (or thermoplastic as defined herein) in the sense that it isthermoformable, i.e., able to be elongated under heat without crackingor degrading its conductivity. Use in an SMC process, vacuum formingcontact with a heated tool, or other high temperature mold faceapplications can require a higher temperature resistance of the finishedprimer coat. The resin is dissolved in a suitable organic solvent andapplied as a thin uniform film coating. The conductive coating is thendried by solvent evaporation at elevated temperatures to cure and hardenthe resin and form a thin, flexible, continuous uniformly conductiveprimer coat across the surface area of the release coated carrier. Thebase resin can be modified to accommodate adhesion to differentplastics. In addition, other conductive materials such as graphite,nickel, copper, silver coated glass beads, nickel coated graphitefibers, and a metal flake known as Metalure (a trademark of AveryDennison) can be added to the resinous primer base to alter conductivityas desired. A minor amount of an anti-blocking agent such as fumedsilica is dispersed in the mixture. The dispersion is reduced to pressviscosity with the organic solvent until a viscosity of about 1,000 cpsis achieved at approximately 24% solids. A suitable organic solvent canbe a 1:1 mixture of methyl-ethyl-ketone (MEK) and toluene. To assurethat the lacquer meets conductivity requirements, the surfaceresistivity is preferably checked with both an ohm/volt meter and aRansberg Model 236 sprayability meter. The ohm/volt meter shouldpreferably read in the range of 5 K-ohms to 50 K-ohms/inch. The Ransbergmeasurement should be greater than about 110 units. The lacquer can bechecked by drawing down small samples, baking them at 200° F. for fourminutes to drive off the solvent, and then measuring the conductivity.Once conductivity requirements have been met, the conductive primer coatcan be applied to the matte release carrier.

FIG. 3 shows in more detail a first step in the process which includescoating the matte release coat in thin film form onto the surface of thetemporary carrier film. The film thickness of the carrier film is lessthan about two mils, and is preferably about 0.48 to about 0.75 milthick. The carrier film also has a film thickness which providessufficient strength to permit its release from the conductive coating.

The carrier film is contained on a supply roll 38 from which the carrieris unwound, passed around an idler roller 40, and then passed to agravure print station 42 where the matte release coat is gravure-coatedonto the carrier film by a conventional gravure cylinder 44. The carrierfilm containing the matte release coat is then passed through a firstdrying oven 46, preferably a 20-foot long impinging air oven operated ata temperature from about 325° to about 350° F., sufficient for dryingand cross-linking the matte release coat 20. In the first stage dryingoven, the matte release coat is sufficiently cross-linked to permanentlybond it to the carrier sheet. Preferably, the matte release coat iscoated and dried to produce a coat weight (dry) from about 3 to about 5gr/m².

The carrier containing the matte release coat which has been dried andcross-linked exits the first stage oven 46 and is then passed to areverse-roll coater station 48 for coating the conductive primer coat 24onto the dried matte release coat. The conductive primer coat is thenpassed to a second drying oven 50, preferably a 120-foot long impingingair oven. This oven can be in multiple stages with drying zones ofdifferent controlled temperatures, depending upon the dryingcharacteristics of the conductive primer coat. Preferably, the castconductive primer coat, described below, is dried at an oven airtemperature of about 250°-350° F., depending on resin selection, to forman essentially solvent free (<0.3% by weight) electrostaticallysprayable and electrically conductive coat on the matte release film.

The dried, conductive-coated film 51 is removed from the second dryingoven 50 and wound onto a rewind roll 52 at the output of the firstcoating stage.

The conductive coated side of the film can be coated with the size coat27 for use in later bonding the conductive layer to a face sheet duringa transfer-lamination stage of the process. For certain laminationsheets and laminating conditions the size coat may be omitted.

The film containing the dried conductive coat passes from the seconddrying oven 50 to a gravure print station (not shown) where an optionalsize coat 25 is coated on the dried conductive coat. The size coat isthen passed through an impinging air oven (not shown) operated at atemperature of about 250° F. for drying the size coat 25. The size coatis applied using a gravure cylinder and can contain a pigment up toabout 25% by volume, although less than 10% by volume is preferred. Thedried coat weight of the size coat ranges from about 1 to about 3 gr/m².

The size coat 25 can comprise any of various suitable coatingcompositions to provide adhesion of the conductive film to the facesheet 26 during the transfer-lamination step carried out later duringthe process. The size coat preferably comprises a suitable thermoplasticresinous material such as an acrylic resin. In one embodiment, the sizecoat comprises a polymethylmethacrylate orpolyethylmethacrylate-containing resin.

In certain instances in which the face sheet 26 may be made from athermoplastic polyolefin such as polypropylene or polyethylene, adifferent size coat can be used. In this instance, the size coat ispreferably made from a coating composition of a solution of athermoplastic chlorinated polyolefin (CPO). A preferred CPO size coatpreferably is a chlorinated polypropylene or chlorinated polyethylene,in which the coating composition contains about 10% to about 60% byweight of the CPO, and correspondingly, about 40% to about 90% by weightsolvent.

Following drying of the size coat 25, the conductive film exits thedrying oven and is wound on a supply roll (not shown). The completedfoil is then removed from the coating system and installed at the unwindof a transfer-laminating station for removing the conductive primer 24and size coat 25 from the release-coated carrier and transferring theprimer to the surface of the face sheet 26. This step can be in severalalternatives. An extruder-laminator can be used, in which the face sheet26 is extruded, while simultaneously, the conductive primer film islaminated to the extruded sheet, using the heat and pressure generatedfrom the extruder die exit and calander and transfer rolls to heat-bondthe primer film to the sheet. This approach is shown in FIG. 11 anddescribed in more detail in Example 15. When the conductive foil ispressed into contact with the extruded sheet, the extrusion temperatureis also sufficiently elevated to bond the foil to the extruded sheet.The matte release coated polyester carrier sheet has a heat resistancesufficient to resist elongation or deformation during the transfer andlamination step. Following the lamination step, the flexible, laminatedextruded film undergoes controlled cooling. A series of water-cooledchill rollers (not shown) produce a controlled temperature reduction inthe laminate.

Alternatively, an existing primer-coated face sheet can be extrusion caplaminated to an extruded sheet as shown in FIG. 10 and described in moredetail in Example 10. This technique is also shown generally in FIG. 2in which the extruded substrate 28 is a multi-layer extrusion. In someinstances, particularly those involving high temperature engineeringplastics such as polyarylates in a multi-layer substrate form, adhesionis obtained without the size coats 25 or 27.

As another alternative, the conductive primer can be laminated to anexisting semi-flexible plastic face sheet by a dry painttransfer-lamination step described in Example 1.

When the carrier is removed from the laminate, the matte release coat,which has been cross-linked and permanently bonded to the carrier sheet,remains adhered to the carrier film during the stripping process. Thematte release coat has a matte outer surface with a micro-roughnesswhich is transferred to the conductive primer coat. The micro-roughnessof the matte coat is replicated to transfer a sufficiently low gloss tothe primer coat to enhance spray paint adhesion. The desired gloss levelcan vary. The formulation of the matte release coat (described below)provides a combination of the desired low gloss surface, together with asmooth or free release of the carrier sheet from the low gloss surfaceat any stripping temperature.

The matte release coat formulation comprises a coating which can beapplied to the carrier by conventional casting techniques, such asgravure or roller coating. The preferred coating composition is athermosetting resinous material which, when exposed to heat for dryingit, also cross-links and permanently bonds as a surface film adhered tothe carrier sheet. The solids contained in the matte release coatpreferably include, as a principal component, one or more cross-linkingagents to provide good adhesion of the dried cross-linked coating to thepolyester carrier film. In one embodiment, the matte release coatformulation includes a primary cross-linking resin such as a vinyl resinthat bonds to the polyester film. A suitable vinyl resin is a mediummolecular weight vinylchloride-vinylacetate resin known as VAGH,described in more detail in Example 1 below. This vinyl resin can bepresent in an amount up to about 20% of the total solids in the matterelease coat. In addition, the matte release coat can include asecondary cross-linking resin to improve release of the conductive coatfrom the matte release coat. In one embodiment, the secondarycross-linking resin can be an acrylic modified alkyd resin such as theresin known as Chempol 13-1501 also described in more detail inExample 1. This secondary cross-linking resin comprises from about 1% toabout 15% of the total solids of the matte release coat. The matterelease coat further includes a suitable catalyst for accelerating thecross-linking process, typically comprising from about 1% to 2% of thetotal solids in the matte release coat.

The resinous components of the matte release coat composition are mixedwith suitable organic solvents. In one embodiment, the resins are mixedwith a primary resin solvent such as methyl isobutyl ketone (MIBK) whichcomprises about 80% to about 95% of the total solvent in theformulation. A secondary resin solvent such as isopropyl alcohol (IPOH)is useful in retarding cross-linking of the resins in solution. Thesecondary resin solvent preferably comprises from about 5% to about 20%of the total of solvent.

The matte release coat formulation is prepared by dissolving the primarycross-linking resin in the primary and secondary resin solvents bymixing and then adding the secondary cross-linking resin, together witha primary matting agent, preferably in the form of a filler comprising afine particulate inert inorganic material. In one embodiment, the fillercomprises aluminum silicate with an average particle size of about 5.0microns. The filler contained in the formulation comprises up to about25% of the total solids in the matte release coat. The fine particulatefiller is thoroughly dispersed in the resin and resin solvent blend,preferably under elevated temperatures from about 100° to about 120° F.

When the matte release layer dries and cross-links, it forms a mattecoating on the surface of the carrier sheet. The thermoset resinouscoating is continuous with the face of the carrier sheet, and in itscross-linked and permanently bonded dry film form, it provides a hightemperature resistant thermal transfer barrier between the polyestercarrier sheet and the primer coat and its underlying substrate. Thematte surface is controlled by the amount and particle size of thefiller. The fine particles in the matte release coat form, on amicroscopic scale, a surface with a micro-roughness that transfers areplicated micro-roughness to the surface of the dried conductive coat.

The matte release coat formulation may include a release agent toenhance freely releasing the carrier and its matte release coat from theconductive coat during the transfer process. The release agentpreferably includes a wax component such as a polyethylene wax whichmelts at elevated temperatures to allow easy hot release of the releasecoat. The wax component is normally suspended in the matte release coatat 100°-120° F.; and the wax component, in its suspended or particulateform, also acts as a matte agent. The preferred polyethylene wax isShamrock S-381-N1 (described in Example 1 below). In one preferred formof the release coat formulation, the polyethylene wax comprises fromabout 0.1% to about 25% of the solids contained in the matte releasecoat.

The release agent contained in the matte release coat formulation mayfurther include a silicone resin component which combines with thepolyethylene wax to enhance free release of the conductive coat from thematte release coat at temperatures ranging from room temperature toelevated.

In one embodiment, the silicone resin comprises from about 0.5% to about25% of the solids contained in the matte release coat formulation.Release is improved when the wax and silicone resin are used incombination in the matte release coat.

In one embodiment, the conductive primer coat is a thermoplasticsynthetic resinous coating composition. The preferred dry film thicknessof the conductive coat is from about 0.3 to about 1.5 mils. Preferably,the conductive primer coat lacquer formulation produces a dry filmcoating having desired properties of electrical conductivity, resistanceto spray paint solvents, and adhesion to sprayed paints and primers,resulting in a Class "A" surface after electrostatic paint spraying. Theelectrically conductive polymeric material, in one embodiment, includesa polyester resin containing a fine particulate conductive material,such as carbon black, and an anti-blocking agent, such as a dispersionof fumed silica. Other thermoplastic resinous materials can be used suchas acrylics, polyurethanes, polyarylates, polycarbonates, andpolyetherimides.

In one embodiment, a principal component of the resin contained in theconductive primer coat is a polyester resin, such as Adcote X80-125 (atrademark of Morton International of Chicago, Ill.). In its preferredform, the polyester component comprises from about 50% to about 90% ofthe total solids contained in the conductive coat formulation,preferably from about 70% to 85%. The lower limit is governed by thecohesive strength of the dried film and the upper limit is governed bythe conductivity required. In one embodiment, the conductive coating islightly cross-linked, as mentioned previously, to increase thetemperature resistance of the finished primer, as described below inExample 15.

A second component is a conductive pigment, preferably a carbon black,and most preferably Vulcan XC-72 a trademark of Cabot Corp. In itspreferred form the carbon black comprises from about 10% to about 50% byweight of the solids contained in the conductive primer. The lower limitis governed by the surface conductivity of the finished dried conductiveprimer film which will allow electrostatic painting.

The third, and optional, component is a particulate antiblocking agent,preferably a fumed silica, most preferably the material sold under thedesignation TS-100, a trademark of DeGussa. In its preferred form, thefumed silica comprises from 0% to about 5% by weight, most preferably 2%to 3% by weight, of the total solids in the conductive primer. Too muchantiblocking agent reduces the conductivity of the finished, driedconductive primer film.

A preferred formulation contains 27 parts Adcote X80-125 polyester resin(dry), solvents MEK and toluene 32.6 parts each, 6.8 parts Vulcan XC-72carbon black, and one part TS-100 fumed silica.

Other minor components of the conductive coat formulation may include adispersing agent, such as the material sold under the designationFC-430, a trademark of 3M Co. The dispersing agent preferably comprisesup to about 0.05 parts per 100 parts resin.

EXAMPLE 1

A plastic car body panel was made by the following steps: (a) preparinga matte release film; (b) preparing a conductive primer film; (c)preparing a conductive transfer foil; (d) transfer to a thermoformablebacking sheet; (e) thermoforming; and (f) bonding of the thermoformedlaminate to a substrate panel.

a. Matte Release Coat

A matte release coat was formulated from the following components:

    ______________________________________                                                  Component       Parts                                               ______________________________________                                        Composition 1:                                                                            Methyl isobutyl ketone (MIBK)                                                                   42.4                                                        Isopropyl alcohol (IPOH)                                                                         7.8                                                        VAGH              10.2                                                        ASP400            26.3                                                        Chempol 13-1501   12.7                                                        S381-N1            0.6                                                                          100.0                                           Composition 2:                                                                            Methyl isobutyl ketone                                                                          56.7                                                        Isopropyl alcohol  9.0                                                        VAGH              15.1                                                        Chempol 13-1501   19.2                                                                          100.0                                           Release Coat:                                                                             Composition 1      25.35                                                      Composition 2      54.83                                                      SR107              0.86                                                       MIBK/IPOH Blend (85/25)                                                                          7.56                                                       Cycat 4040         4.2                                                        Cymel 303          7.2                                                                          100.00                                          ______________________________________                                    

1. VAGH is a medium molecular weight, partially hydrolyzed vinylchloride-vinyl acetate resin (approximately 90% vinyl chloride, 4% vinylacetate and a hydroxyl content of 2.3%) sold by Union Carbide, Somerset,N.J.

2. ASP400 is an aluminum silicate of average particle size five micronsmade by Engelhard Corp., Edison, N.J., and sold by Jensen-Souder,Itasca, Ill.

3. Chempol 13-1501 is an acrylic modified alkyd resin solution (50%resin, 50% xylol) sold by Freeman Chemical Co., Port Washington, Wis.

4. SR-107 is a silicone resin manufactured by General Electric,Waterford, Connecticut, and sold by Fitzchem, Chicago, Ill.

5. S381-N1 is a polyethylene wax sold by Shamrock Chemicals Corp.,Newark, N.J.

6. Cycat 4040 is a para toluene sulfonic acid catalyst (40% by weight inisopropanol) sold by American Cyanamid Co., Walingford, Conn.

7. Cymel 303 is a liquid hexamethoxy-methylmelamine cross-linking agentsold by American Cyanamid.

Composition 1 was produced by dissolving the VAGH resin in an MIBK andIPOH blend by mixing in a Cowles mixer and then adding the Chempol13-1501, ASP400 and the S381-NI while mixing. This mixture was thensandmilled at a temperature of about 110° F. to disperse the ASP400.

b. Conductive Primer Coat

A conductive primer coat was formulated as follows. 16.5 parts of methylethyl ketone (MEK) and 16.5 parts of toluene were mixed in a vessel. 58parts of the polyester resin solution were slowly added while mixing.After the mixture was homogeneous, 9 parts of Vulcan XC-72 carbon blackwere slowly added. This premix was then milled to a grind of less than 5microns in a shot mill (1 mm shot). Any solvent loss during milling wasbrought back to its original weight, and the batch was labeled Batch A.96 parts of the polyester resin solution were added into a separatevessel and mixed while slowly adding 4 parts fumed silica. The mixturewas dispersed to a grind of 30 microns and labeled Batch B. Three partsBatch A and one part Batch B were mixed until a homogeneous state wasachieved.

8. The polyester resin solution comprised Adcote X80-125 which was at40% solids in a 50:50 blend of MEK and toluene.

9. Vulcan XC-72 is a high surface area conductive carbon black ofaverage particle size of 30 nm sold by Cabot Corp. of Waltman, Mass.

10. The fumed silica was TS-100 with an average particle size of 5microns, sold by Degussa Corporation of Teterboro, N.J.

c. Preparation of the Conductive Transfer Foil

The matte release coat was gravure coated in uniform film thickness ontothe carrier with a 100 HK gravure cylinder pattern at a coat weight(dried) of 3 gr/m². The carrier was 75 gauge oriented gloss polyestercarrier sheet (Hostaphan 2000, sold by Hoechst Celanese, Greer, S.C.).Line speed was 200 feet per minute and the coating was dried andcross-linked in a 20 foot impinging-air oven (Oven No. 1 in FIG. 3) atan air temperature of 340° F. (web temperature approximately 220° F.).This formed a continuous, uniform high temperature resistant matterelease film permanently bonded to the carrier sheet.

Next, the conductive primer coat was coated at a coating weight (dried)of 22 gr/m² onto the dried matte release coat in a reverse-roll coaterstation on the same coater. The primer coat was of continuous, uniformfilm thickness and was dried and fused in a 120 foot three-zoneimpinging air oven with the air temperatures in the three zones being200° F., 230° F., and 250° F. This formed a dried conductive primer coaton the matte release coat of the carrier film.

To minimize web shrinkage and avoid distortion of the carrier film, webtension was maintained below 0.8 lbs/linear inch of web width throughthe drying ovens.

The dried, coated primer film was wound as a roll, and removed from thecoater.

d. Transfer to Thermoformable Backing Sheet

The conductive primer-coated carrier was next laminated to thethermoformable face sheet 26 by dry paint transfer-laminating techniquesillustrated in FIG. 4. The thermoformable laminate 56 formed by thetransfer-lamination step includes the composite conductive primer layer24 adhered to the face sheet 26. The face sheet is preferably asemirigid, self-supporting, thin, flat sheet of a synthetic resinousmaterial. The face sheet is made from a material which is compatiblewith an injection-molded plastic material or thermosetting fiber filledmolding compound later used to form the structural substrate base 28 ofthe finished article, or the face sheet is compatible with anotherpolymeric laminate to which it is adhered when the total structure isvacuum pressure formed as an alternative technique for forming thefinished panel. Preferably, the face sheet is made from the same orsubstantially the same polymeric material as the substrate base of thefinished article. The face sheet also is made from a material having athickness capable of thermoforming into a complex three-dimensionalshape, along with the adhered composite conductive primer coat, withoutsubstantially affecting the conductivity of the conductive primer. Thematerial from which the substrate is molded can contain a substantialamount of large fibers or particulate filler and therefore can producean imperfect surface on the final painted article molded from thesubstrate material. The laminate is adhered to the otherwise imperfectsurface of the molded substrate to improve the surface characteristicsof the substrate panel and produce a uniform conductive primer which,when electrostatic spray painted with an exterior automotive paint,produces an outstandingly smooth controlled exterior Class "A"automotive finish. The properties of a Class "A" exterior automotivepaint surface are described generally in PCT Application No. WO88/07416, incorporated herein by this reference. The multi-layeredarticle in its finished form comprises a high-performance, essentiallydefect-free, three-dimensionally shaped paint coat with exteriorautomotive properties in combination with the backing sheet, whichprovides a buffer layer between the substandard surface of the substrateand the finished paint coat. The face sheet material minimizes thesurface imperfections transmitted to the paint coat. The preferredmaterials from which the face sheet is made are ABS(acrylonitrile-butadiene-styrene), polycarbonate, a polyester known asXenoy (a trademark of G.E.), a polyetherimide known as Ultem (atrademark of G.E.), a modified phenylene oxide known as Noryl (atrademark of G.E.), polyarylate, TPO, nylon, vinyl (PVC), and GTXurethane acrylic polycarbonate. A preferred ABS material is BorgWarner's Cycolac L.S. Thermoplastic polyolefins (TPO's) includingpolypropylenes and polyethylenes may be used, as well as polyesters oran amorphous nylon, such as Bexloy C-712, a trademark of Du Pont.

The thickness of the face sheet can vary, but generally it is necessaryfor the face sheet to have a sufficient thickness to isolate or absorbimperfections in the surface of the underlying substrate whilepresenting a smooth upper surface of the paint coat after painting. Adesirable range of thickness of the face sheet is believed to be fromabout 10 to 200 mils, with 20 mils being a preferred thickness for anABS sheet when used in thermoset or thermoplastic molding, for example.The thicker laminates are preferred for VPF (vacuum pressure forming)operations.

The laminating step illustrated in FIG. 4 shows the conductive-coatedcarrier 60 stored on a top unwind roll 62 and a flexible 20 mil thickABS face sheet 24 stored on a bottom unwind roll 64. Theconductive-coated carrier, in one embodiment, comprises the conductiveprimer coat on a single flexible matte release-coated casting sheet. Theconductive-coated casting sheet 60 is passed around a drum 66, and theface sheet passes around a drum 68. The carrier and backing sheet thenpass between a heated laminating drum 70 and a rubber backup roll 72.The laminating drum is preferably made of steel and is preferablyoperated at a temperature of about 400° to 425° F. It is pressed intocontact with the overlapping sheets to heat them to a temperaturesufficient to melt the release agents in the matte release coat torelease the primer from the carrier and to bond the conductive primercoat to the face sheet. The rubber backup roll 72 and laminating drum 70are in pressure contact with the carrier and backing sheet preferably ata pressure of about 300 pounds per lineal inch. The speed at which thesheets travel during laminating ensures that the resulting laminate isheated to a temperature necessary to effect transfer and bonding. Theheat softens the face sheet material somewhat to ensure a complete bondbetween the conductive coat and the face sheet. The polyester carriersheet of the conductive matte release-coated carrier has aheat-resistance above laminating temperatures so the carrier sheetresists elongation during the laminating step. During the transfer stepthe micro-roughness of the matte surface on the carrier is transferredto the surface of the primer coat. Following the bonding step, theflexible conductive-coated laminate is then passed around one or morechill rollers 74 for cooling the laminate to room temperature. Thefinished laminate 56 then passes onto a laminate rewind drum 76. Thecarrier sheet may be stripped away from the laminate prior to thesubsequent thermoforming step or may remain attached. Other polymericfilms or laminates may also be similarly transfer-laminated to thefinished conductive laminate.

e. Thermoforming

In the next step in the process, the laminate 56 shown in FIG. 4 wasthermoformed into a desired three-dimensional shape. The thermoformingstep is illustrated in FIGS. 5 and 6 in which the initially flatlaminate is formed into a highly contoured three-dimensional shape foruse as the surface of a car body panel. Separate laminate sheets areindividually placed inside a clamping frame 78 of a vacuum-formingmachine. The clamping frame is movable back and forth on a track 80. Thelaminate sheet is initially placed in the clamping frame at the positionshown in FIG. 5.

The clamping frame is then moved along the track into an oven 82 forheating the back sheet to a thermoforming temperature. The ABS facesheet is heated to a temperature in the range of about 280° to about380° F. For a Bexloy nylon the sheet is heated to a temperature fromabout 380° to about 420° F. These temperatures are actual sheettemperatures, not oven temperatures. A pressure assist can be used withthe thermoforming step in order to reduce the thermoforming temperature.At thermoforming temperatures the laminate sags as shown at phantomlines at 84.

After the laminate is heated in the oven to the desired temperature, theclamping frame is moved back along the track 80, away from the oven 82and to its original position above a vacuum-forming buck 86. The workingsurface of the vacuum-forming buck 86 is shown as a curved surface, byway of example only. Other configurations can be used depending upon thedesired three-dimensional shape imparted to the surface of the finishedarticle.

The preheated laminate is next vacuum-formed into the desiredthree-dimensional shape by first drawing a vacuum on the vacuum-formingbuck through its connection to a vacuum pump 88. The vacuum-forming buckis then raised to the position shown in FIG. 6, where it has risen intothe clamping frame. The vacuum is pulled through holes in the buck toforce the hot plastic into the shape of the working surface of the buck.Positive air pressure can be applied to the free face of the primer coaton the opposite side of the buck to increase forming pressure. The buckstays in place long enough to cool the plastic to a solid state againbefore the buck drops away back to the position shown. This leavesbehind the plastic in the shape of the buck. The preferredvacuum-forming step is to use a male vacuum former in which thevacuum-forming buck is in direct contact with the face sheet so as tonot contact the exterior conductive coat on the opposite side of thebacking sheet. In this way, the face sheet hides most of any of thepossible defects in the working surface of the buck; and the surface ofthe conductive coat is not affected, but is allowed to elongate freely.Female molds can also be used successfully.

In an alternate thermoforming step (not shown), the laminate can be fedto the thermoformer as a continuous sheet. The laminate first passesthrough the oven and then passes to the thermoforming buck in line withthe downstream end of the oven. The continuous sheet is stopped atpreset intervals for heating the laminate to the thermoformingtemperature while a previously heated portion of the sheet is vacuumformed into the desired shape.

The thermoforming step produces a three-dimensionally shaped preformedlaminate shown at 90 in FIG. 7. For simplicity, the preformed laminateis illustrated as comprising the face sheet 26 and the conductive primercoat 24 adhered to it. The laminate is illustrated in athree-dimensionally shaped form following the thermoforming step as oneexample only of a possible three-dimensional shape. Other complexthree-dimensional shapes are also possible. The conductive coatingexperiences elongations greater than about 150% during thermoformingwithout significantly affecting the uniformity of conductivity and theability to electrostatically spray paint it to achieve a Class "A"surface.

(f) Bonding of Thermoformed Laminate to Substrate Panel

A subsequent injection-cladding operation is shown in FIGS. 7 and 8 inwhich the preformed laminate 90 is adhered to an underlying plasticsubstrate panel 28. The injection-cladding step is an example of apossible means for adhering the laminate to the substrate. After thelaminate 90 is preformed to its desired shape, it is trimmed to size andis ready for injection-cladding. The thermoformed laminate 90 is placedin an injection mold 92 and fused to the face of an injection-moldedsubstrate. According to a first step in the injection-cladding step, aplastic injection mold is in its open position, and the preformedlaminate is placed in a mold cavity 94 between front and rear moldhalves 96 and 98. The inside surface 100 of the mold half identicallymatches the exterior contour of the conductive primer-coated surface ofthe preformed laminate 90. This surface of the mold is a rigid surfacewhich is free of surface defects so that surface defects are nottransferred to the conductive-coated surface of the laminate. After thevacuum-formed die cut sheet 90 is placed inside the injection mold, aspace is left behind the laminate for receiving the injection moldingmaterial 102. The injection molding material flows through a passage 104in the rear mold half and into the mold cavity behind the preformedlaminate. The molding material conforms to the shape of the mold cavityand is permanently fused to the face sheet portion of the laminate. Theinjection molding material does not come into contact with theconductive coat. As described previously, the molding materials fromwhich the substrate and the face sheet are made are compatible so thatthe two materials fuse to form an integral molded substrate on which theconductive coat provides a defect-free finish. The temperature at whichthe injection-mold is operated is substantially below the melttemperature of the molding material. In one embodiment, in which an ABSbacking sheet was used, the molten material was at a temperature ofabout 450° F., for example. A water jacket can be used to cool the facesof the mold. Both faces of the mold are cooled to a temperature in therange of about 160° to 170° F., so that the conductive primer coat onthe laminate remains stable during injection molding. A lightlycross-linked or more temperature-resistant resin can be used at highermold temperatures.

The finished article produced by the process of this invention includesthe preformed laminate 90 and its face sheet 26 which have been fused tothe molded substrate.

In one embodiment, the article can be a conductive primed exterior carbody member or panel. Any defects in the substrate material have beenabsorbed by the 20 mil thick face sheet to provide a defect-freeconductive coat 22.

Although this example has been described with respect to the illustratedthermoplastic injection-molding steps, other techniques can be used forforming the finished article. These include, but are not limited to,fiber reinforced thermoset injection molding (TMC), use of sheet moldingcompounds (SMC), compression cladding and reaction injection molding(RIM) and resin transfer molding (RTM) techniques, vacuum pressureforming, and pressure-sensitive or adhesive bonding techniques. Otherplastic molding materials also can be used in place of ABS for fusingthe substrate panel to the primer-coated face sheet. These may includethermoplastic polyolefins (TPO's) such as polypropylenes andpolyethylenes; polyesters; and amorphous nylon. In these instances, theface sheet is preferably made from the same polymeric material as theinjection molding material.

EXAMPLE 2

The conductive coating in the polyester resin system from Example 1 wascoated as a uniform film 0.8 mils thick on the matte release coatedpolyester film in Example 1 and then laminated to a 20 mil thick ABSface sheet.

The following table shows resistivity measurements in Ransberg units,K-ohms/in., and K-ohms/sq.

    ______________________________________                                        Film Thickness                                                                           Ransberg    K-ohms/in.                                                                              K-ohms/sq.                                   ______________________________________                                        0.8 mils   165+        37        26                                           ______________________________________                                    

EXAMPLE 3

The conductive coating in the polyester resin system from Example 1 wascoated as a film 0.5 mil thick on the matte release coated polyesterfilm in Example 1 and then laminated to a 20 mil thick ABS backingsheet.

The following table shows resistivity measurements in Ransberg units,K-ohms/in., and K-ohms/sq.

    ______________________________________                                        Film Thickness                                                                           Ransberg    K-ohms/in.                                                                              K-ohms/sq.                                   ______________________________________                                        0.5 mils   165+        45        32                                           ______________________________________                                    

In both Examples 2 and 3, the coating resulted in a surface that iselectrostatically sprayable. To be considered electrostaticallysprayable a Ransberg reading greater than about 110 units is required.

The most practical method to determine electrostatic sprayability iswith the Ransberg 236 sprayability meter. Two conductive probes that areone inch apart contact the surface under test. The measurement isactivated by depressing a button on the hand-held gauge and anelectrical charge is passed from one probe to the other. The reading isrecorded in Ransberg units. Any reading below 110 units is considered asurface that is not electrostatic sprayable.

Another method for calculating the surface resistivity is by the use ofa Micronta 22-201U ohm/volt meter. The preferred method is by point topoint readings recorded by fixing the distance of the point probes atexactly one inch apart, contacting the test surface with the probes, andrecording the resistivity in K-ohms/inch. The most preferred method isby fixing two one-inch by 1/8 -inch copper bars on a 11/4 inch squareblock of non-conductive plastic such as plexiglass. The bars areparallel, one inch apart. The copper bars serve as contact points forthe surface to be measured. Each bar is wired into the ohm/volt meterand a 500 gram weight is placed on the top of the plexiglass before thereading is recorded in K-ohms/square.

EXAMPLE 4

A series of conductive coatings were formulated at different carbonblack pigment to polyester resin ratios. The conductive coatings wereapplied to a matte release liner as described in Example 1 and laminatedto a 20 mil thick ABS sheet. The conductive film thickness was 0.8 mils.The carbon black was Vulcan XC-72. The following table shows surfaceresistivity measurements as a function of pigment/binder (or resin)ratios. The ratio is determined on the basis of a dry film resin.

    ______________________________________                                        P/B Ratio                                                                              Ransberg     K-ohms/in                                                                              E.S. Sprayable                                 ______________________________________                                        0.2308   +165          25      Yes                                            0.2129   +165          46      Yes                                            0.1953   +165          97      Yes                                            0.1778   164          378      Yes                                            0.1606   147          500      Yes                                            0.1416   140          500      Yes                                            0.1211   131            500+   Yes                                            0.0895    87            500+   No                                             ______________________________________                                    

EXAMPLE 5

Standard Cabot Vulcan XC-72 carbon black having a surface area of 254 M²/gm was compared to two other Cabot lower surface area carbon blacks.Mongul L having a surface areas of 138 M² /gm and Vulcan PA-74 having asurface area of 140 M² /gm were formulated at 7 parts carbon black per30 parts polyester resin. The formulas were milled with 1/8 inch shot ona lab scale paint shaker for three hours. The coatings were applied tothe matte release liner as described in Example 1 at a thickness of 0.8mils.

The following results represent carbon black type vs Ransberg unitsmeasurements:

    ______________________________________                                        Carbon Type    Ransberg E.S. Sprayable                                        ______________________________________                                        Mongul L       81       No                                                    Vulcan XC-72   165+     Yes                                                   Vulcan PA-74   82       No                                                    ______________________________________                                    

It was concluded that carbon black having a surface area greater thanabout 200 m² /gm would produce the highest and most consistentconductivity.

EXAMPLE 6

Conductive materials other than carbon black were formulated. U.S.Bronze Powder Palegold B620 and Potter Labs ESD fiber batch 91-100-4.6.7were substituted in the polyester resin of Example 1 at a concentrationof 30% by weight (dry). After the mixture was homogeneous, the solutionswere coated at a film thickness of 0.8 mil. The following results showmaterial type compared with Ransberg units of conductivity:

    ______________________________________                                        Material Type  Ransberg E.S. Sprayable                                        ______________________________________                                        Bronze Powder  80       No                                                    ESD Fiber      82       No                                                    ______________________________________                                    

EXAMPLE 7

Samples of the conductive coating of Example 1 with U.S. Bronze PowderPalegold B620 added at 50% and 67% by weight levels in place of thecarbon black were applied to matte release liner as described in Example1 at a film thickness of 0.8 mils and laminated to a 20 mil thick ABSsheet. Similar samples were made with no conductive filler, with carbonblack as the conductive filler, and with Metalure as the conductivefiller. The Metalure material was Avery Dennison product no. L-55350.The samples were measured for EMI/RF shielding properties with aBekiscan CP2 instrument. The Bekiscan CP2 microwave reflection analyzeris a non-destructive method of testing EMI/RF shielding effectivenessfor plastic parts. Good commercial products have reflection measurementsin a range above about 70%. The following table shows the test results:

    ______________________________________                                                        Shielding                                                     Sample          At 10 Ghz    K-ohms/sq.                                       ______________________________________                                        ABS Only         0% Refl.    >10.sup.12                                       Conductive Coat with                                                                           0% Refl.      10.0                                           carbon black on ABS                                                           Conductive Coat 48% Refl.      0.21                                           with 50% by weight                                                            bronze powder                                                                 Conductive Coat 71% Refl.      0.12                                           with 67% by weight                                                            bronze powder                                                                 Conductive coat with                                                                          90% Refl.    N.A.                                             Metalure at 30% by weight                                                     ______________________________________                                    

Good results were obtained with the greater sized Metalure flakes whichare high aspect ratio vacuum metallized aluminum flakes with an averagemajor dimension of about ten microns.

EXAMPLE 8

The conductive laminate of Example 1 was formed on a 20 mil thick ABSsheet. The laminate was vacuum formed (on a Packaging Industriescontinuous feed vacuum former) into a vacuum formed shell. The shell wasinjection molded with ABS in an injection molding machine. The resultingsubstrate was shaped as a finished door trim panel. The following tablelists the resistivity measurements on the surface of the finished part:

    ______________________________________                                        Part   Ransberg K-ohms/in.  K-ohms/sq.                                                                            Sprayable                                 ______________________________________                                        Trim   165+     10.3        7.1     Yes                                       ______________________________________                                    

EXAMPLE 9

A conductive coating as described in Example 1 was applied to a matterelease liner as described in Example 1 and laminated to a 20 mil thickABS sheet and a 20 mil thick Ultem sheet. Each construction was vacuumformed with a three-step tool that simulated three different depths ofdraw or elongation. The following table shows surface resistivitymeasurements as a function of depth of draw or final film thickness ofthe conductive coating:

    ______________________________________                                        Depth  Film                         E.S.                                      of Draw                                                                              Thickness                                                                              Ransberg    K-ohms/in.                                                                            Sprayable                                 ______________________________________                                        ABS 20 Mil                                                                    Lo     0.8 mil  165+        35      Yes                                       Med    0.6 mil  165+        38      Yes                                       Hi     0.5 mil  165+        45      Yes                                       Ultem 20 Mil                                                                  Lo     0.8 mil  165+        35      Yes                                       Med    0.6 mil  165+        45      Yes                                       Hi     0.4 mil  165+        55      Yes                                       ______________________________________                                    

After recording data, the conductive coated vacuum formed laminate waselectrostatically spray painted. The paint used was received directlyfrom the GM assembly paint line at the Cadillac assembly plant in LakeOrion, Mich. The following table lists the individual paints:

    ______________________________________                                                                     Film                                             Paint         Identification Thickness                                        ______________________________________                                        Grey Prime    PPG Code 13 Prime                                                                            1.2 mils                                                       1146-9855 Lot 19563                                             Base Coat     PPG Code 22 Blue Met                                                                         0.9 mils                                                       8966 Lot 17733                                                  Urethane Clear Coat                                                                         Part A - PPG NCT 2BR                                                                         1.9 mils                                                       Lot 19261                                                       Urethane Clear Coat                                                                         Part B - PPG NCT 2AV                                                          Lot 18423                                                       ______________________________________                                    

The urethane is a clear coat system that is catalyzed when bothcomponents are mixed and sprayed to form a hard clear coat.

The following table represents a GM paint cycle the conductive finishedpart passes through during electrostatic spraying. Prior toelectrostatic spray painting, the surface of the conductive coated partis submerged in a 90° F. ELPO plating bath for five minutes. (ELPO is atrademark of PPG.) The paint then passes through a high voltage sprayhead which charges the paint droplets. The paint then adheres to thegrounded surface without significant over-spray. Both laminate andinjection molded parts were painted according to the bake cyclesdictated by the GM paint line specifications. The grey surface prime wasfirst sprayed at a dry coat weight of 1.2 mils and baked at 250° F. for20 minutes. Then the blue metallic color base coat was sprayed at a coatweight of 0.9 mils and was exposed to a heat at 160° F. for threeminutes. Then the activated clear coat was sprayed on at a coat weightof 1.9 mils and was baked at 250° F. for thirty-nine minutes for thefinal cure. The result was a Class "A" finish that was tested to GM4350M exterior paint specifications. The majority of the testing wasessentially complete including the most critical cycle testing. Thepainted surface has passed each test segment of the specification. Theparts have passed the Xenon Arc SAE J1960 specification. Test resultsare summarized as follows:

    ______________________________________                                        Test  Index   Description  Method   Results                                   ______________________________________                                        A     4.2.1   Initial Adhesion                                                                           GM9071P  99+%                                                    610 tape                                                        B     4.2.9   Knife Crosshatch                                                                           GM9502P  B(Pass)                                                 610 tape                                                        C     4.2.2   Humidity Resist.                                                                           GM4465P  Pass                                                    & Adh. 610 tape                                                                            96 hours 99+%                                      D     4.2.5   Chip Resist. GM9508P  GM 9                                                    min. rating of 7                                                E     4.2.7   Dime Scrape  GM9506P  Good Adhesion                             F     4.2.6   Thumbnail Hardness                                                                         GM9507P  Not Marred                                              no marring or                                                                 paint removal                                                   G     4.2.8   Cure Test    GM9509P  Rating "0"                                H     4.2.11  Gasoline Puddle                                                                            GM9500P  Pass                                      I     4.2.12  Gasoline Dip GM9501P  Pass                                      J     4.2.10  Mandrel Bend GM9503P  N/A                                                     rating pf 0                                                     K     4.3.7   Abrasion Resist.                                                                           GM9515P  N/A                                                     CS10 wheels                                                     L     4.3.4   Cold Crack/  GM9505P  (No effect)                                             Corrosion Cycle       Pass                                                    15 cycles/method A                                              M     4.3.5   Color Crock  GM9033P  U/T                                                     ten complete turns                                              N     4.3.6   Oven Aging   GM9504P  Pass                                      O     4.3.10  Pencil Hardness                                                                            ASTM     Gouge-H                                                 Test         D3363    Scratch-B                                 P     4.3.11  Oil Immersion                                                                              Para.    Pass                                                                 4.3.11                                             Q     4.3.2   Weatherometer                                                                              SAE J1960                                                                              None                                                    Exposure - Xenon                                                              arc 1,000 hours                                                 R     4.3.1   Florida Exposure                                                                           GM4350M  U/T                                                     2 years 5°                                                             facing south                                                    ______________________________________                                    

EXAMPLE 10

Referring to FIG. 10, a 0.8 mil thick conductive coating 22 described inExample 1 was coated on a matte release liner 20 also described inExample 1. The matte release film was laminated to 48 inch wide Lexan,Ultem, and Xenoy sheets. The rolls of laminate shown at 108 wereextrusion cap sheet laminated and vacuum formed. Each conductivelaminate roll 110 was mounted on an extruder 112. The Xenoy sheet caneither be a monolayer extrusion or a 3-5 layer coextrusion with one ormore of the layers being filled. The total layer thickness can bebetween 10 and 200 mils thickness. In this trial, a tri-layer extrusion114 was formed 150 mils in thickness through a 48" wide die lip. Such atri-layer extrusion is shown in the embodiment of FIG. 2 in which theextruded layers can be unfilled Xenoy 28a, glass-filled Xenoy 28b andunfilled Xenoy 28c. Referring again to FIG. 10, the conductive laminatewas fused to the surface of the extrudate 114 with the heat of theextrudate and the pressure at the nip of the metal rollers 116 and 118.The result was a 170 mil thick conductive sheet 120 ready for vacuumpressure forming into a finished electrostatic sprayable part. Thefollowing composites were successfully extrusion laminated and vacuumpressure formed:

    ______________________________________                                        A             B            C                                                  ______________________________________                                        Cond. Coat    Cond. Coat   Cond. Coat                                          20 mil Ultem  20 mil Xenoy                                                                               20 mil Lexan                                      150 mil Xenoy 150 mil Xenoy                                                                              150 mil Xenoy                                      Extrusion     Extrusion    Extrusion                                          ______________________________________                                    

On a smaller scale, the conductive coating as described in Example 1 wascoated on a matte release liner described in Example 1 and laminated toa 150 mil Xenoy coextrusion, resulting in the following construction:

    ______________________________________                                                 D                                                                    ______________________________________                                                 Conductive Coating                                                             25 mil Xenoy                                                                 100 mil glass filled Xenoy                                                     25 mil Xenoy                                                        ______________________________________                                    

Each thick conductive sheet was then vacuum pressure formed on a smallscale die resulting in a contoured conductive finished part that waselectrostatically sprayed as described in Example 9. The conductiveprimer elongated during forming substantially without affecting surfaceconductivity which was sufficiently within the electrostatic sprayablerange. The painted part has passed GM 4350M testing to date. Outdoorweatherability testing is in process, with initial test results showingthat the spray painted parts have passed 1000 hour xenon arc tests.

EXAMPLE 11

Resistivity measurements (in K-ohms/sq.) were made on both a commercialPPG conductive spray-primed fender and a conductive thermoformedlaminate fender of the same shape made by the process of this inventionas described in Example 10. The conductive coating tested was preparedfrom the formulation of Example 1. Forty measurements were recordedrandomly on the surface of each fender. The following table demonstratessignificant statistical improvements in consistency (uniformity of theconductive surface) with the conductive primer (C. Coat) of thisinvention.

    ______________________________________                                        Sample   Mean        Std. Dev.                                                                              6*St. Dev.                                      ______________________________________                                        PPG      56.6        30.2     181.2                                           C. coat  1.1         0.22     1.32                                            ______________________________________                                    

EXAMPLE 12

The following table shows conductive coatings that have beensuccessfully made in alternate resin systems along with correspondingresistivity measurements expressed in Ransberg units. In each resinformulation, Vulcan XC-72 carbon black at a pigment-to-resin ratio of0.23 was added and milled for three hours with 1/8 inch shot:

    ______________________________________                                                           Product          E.S.                                      Resin    Source    No.       Ransberg                                                                             Sprayable                                 ______________________________________                                        Polyarylate                                                                            Hoechst   DKX-103   165+   Yes                                                Celanese                                                             Acrylic  Rohm      B-99      165+   Yes                                                Haas                                                                 Polyether-                                                                             G.E.      Ultem     165+   Yes                                       imide              1000                                                       Urethane Ruco      Rucothane 165+   Yes                                                          Co-A-                                                                         5002L                                                      ______________________________________                                    

No antiblock TS100 fumed silica was used. Each 0.8 mil coating wasapplied to the matte release liner as described in Example 1 andresistivity was measured directly on the web.

EXAMPLE 13

A conductive coating described in Example 1 was applied to a matterelease liner described in Example 1 and was laminated to a 20 mil thickpolyarylate backing sheet. The polyarylate was the DKX-103 material usedin Example 12. The polyester carrier remained on the surface duringsheet molding trials (SMC) for protection. This laminate is only usedfor flat sheet SMC applications such as wallboard decorative panels.Compression molding on this structure resulted in a Ransberg resistivitymeasurement of 165+ units which is electrostatically sprayable.

EXAMPLE 14

A conductive polyarylate film was cast on a two mil thick polyestercarrier. The polyarylate film was made using DKX-57 (Hoechst Celanese)having a T_(g) of about 190° C. The polyarylate conductive film then waslaminated to a 20 mil thick polyarylate sheet. Adequate adhesion andrelease of the carrier were achieved without the use of a matte releasecoat. Conventional lamination was with a thermoplastic size coat such asDu Pont's acrylic 68080 applied at a thickness of 0.3 mils between theconductive polyarylate film and the 20 mil polyarylate laminate toproduce the following structure:

2 Mil Polyester

Conductive Polyarylate

Du Pont 68080 Acrylic Size

20 Mil Polyarylate

The laminate with and without the size coat was vacuum formed into ashell of contoured three dimensional shape. The shell was placed in anSMC mold and compression molded. The shell also can be placed in a TMCmold and plastic injected behind it, resulting in a finishedelectrostatic sprayable part. That is, the conductive primer coat wassufficiently flexible to elongate during vacuum forming, while stillretaining its original level of resistivity; and such resistivity wasreasonably uniform across the surface area of the formed parts. When aflat sheet is desired, either laminate can be placed flat in the moldand compression molded.

EXAMPLE 15

A lightly cross-linked conductive coating was formulated with 2.5 partsDesmodur N100, an isocyanate made by Mobay, Inc., with 100 parts of theconductive coating of Example 1. (The Adcote X80-125 is a polyesterresin with hydroxyl functionality and is capable of being cross-linkedwith isocyanites, melamimes, and other functional resins.) The coatingwas cast on the standard matte release layer at 0.8 mils dry. Bothcross-linked conductive coating and standard conductive coating werelaminated to a high temperature polyarylate plastic sheet. FIG. 11illustrates the extrusion laminating system for high temperaturelaminating the conductive primer film to the extruded sheet. This systemis used when laminating to high temperature plastics, such aspolyarylates, using high temperature-resistant primer films such as thelightly cross-linked film of this example. Referring to FIG. 11, acontinuous extruded sheet 122 of polyarylate is extruded from the dieopening of an extruder 124. The high temperature extrusion is firstpassed between an upper roller 126 and an intermediate level roller 128.The extruded sheet had a thickness of 20 mils. Separately, a hightemperature resistant conductive primer film 130 of this invention isfed toward the extruder from a roller 132. The primer film is carried onthe matte release coated carrier sheet. The primer film and the extrudedsheet are fed to the nip of the intermediate roller 128 and a rubberroller 134 where heat and pressure are applied to soften the coatingsand bond the primer film to the extruded sheet. The temperature of theextruded sheet leaving the die exit opening can be over 600° F., andbonding at the nip of the rollers 128 and 134 can be at temperatures inexcess of 400° F. The conductive primer coated laminate then undergoes atemperature reduction as it passes around a lower roller 136. Afterbonding the primer film to the extrusion, the matte release coatedcarrier is removed, leaving a finished composite sheet 138 comprising ahigh temperature resistant conductive primer film on the exposed face ofthe high temperature resistant plastic sheet. Temperature resistance ofthe conductive surfaces was measured by exposing the coatings to heat at275° F. for one minute on a 6 lb. metal surface, with the followingresults:

Cross-linked--no pickoff, smooth

Standard--pickoff, rough.

The conductive laminate was then thermoformed into a contoured shape.Further tests were made with greater degrees of cross-linking theconductive coat resin. The Desmodur N100 isocyanate cross-linking resinwas added in 6 parts and in 15 parts to two separate vessels eachcontaining 100 parts of the conductive primer formulation of Example 1.The two resins were coated on a matte release carrier and laminated to a20 mil polyarylate backing sheet which was then thermoformed into acontoured shape. The results were as follows:

    ______________________________________                                        Sample        Release Thermoform Shell                                        ______________________________________                                         2 pts/100    OK      OK                                                       6 pts/100    OK      OK                                                      15 pts/100    poor    N.A.                                                    ______________________________________                                    

It was concluded that thermoplastic resins or resins with a small degreeof cross-linking are suitable for use in the conductive coat becausethey can elongate without degrading surface conductivity during moldingor thermoforming. Cross-linking of the polyester resin up to about 10parts cross-linking resin per 100 parts polyester is believed to producea sufficiently thermoplastic conductive coat to retain electrostaticsprayability.

EXAMPLE 16

Four separate conductive primers were made by varying thepigment-to-binder ratio. In this example, the binder was Hypalon 827B, achlorinated polyolefin from DuPont. The particulate conductive fillermaterial was XC-72 carbon black. The formulations are listed below:

    ______________________________________                                                     1    2         3      4                                          ______________________________________                                        Hypalon 827B CPO                                                                             100    100       100  100                                      XC-72 Carbon Black                                                                           23.3   17.5      11.7 5.5                                      Toluene Solvent                                                                              289    289       289  289                                      ______________________________________                                    

Each formulation was made by first dissolving the Hypalon 827B in thetoluene solvent and then dispersing the XC-72 carbon black in the blendusing 1/8-inch steel shot. Each of these solutions was then cast onto amatte polyester carrier sheet at four thicknesses: 0.75 mil, 0.35 mil,0.2 mil, and 0.1 mil.

Each sheet was then laminated to a 20 mil thick TPO panel and the mattepolyester carrier was then removed, leaving a conductive film laminatedto the TPO panel. (The TPO panel is described in more detail in Example17.) Each of these conductive panels was then vacuum thermoformed over amold which gave various elongations over the surface.

The amount of elongation over the areas of the mold was determined bymolding pieces of 20 mil TPO which had an eight line per inch gridpattern. Measurements were taken along the various surfaces of the moldto determine elongations.

Ransberg resistivity and resistivity in K-ohms/square were measuredbefore thermoforming and at six points on the mold after thermoforming.The readings are shown in Table 1 and Table 2, respectively.

Results show very high resistance and no electrostatic sprayability at apigment-to-binder ratio of 0.055 at any film thickness. At apigment-to-binder ratio of 0.117, the 0.1 mil product was not sprayable,and the 0.2 mil product lost sprayability at the higher elongations.

At a pigment-to-binder ratio of 0.175, sprayability was achieved andmaintained until the higher elongations of the 0.1 mil product. At apigment-to-binder ratio of 0.23, sprayability was achieved andmaintained throughout all of the samples and elongations.

The conclusion is that sprayability can be maintained through higherelongations by increasing conductive film thickness and/or thepigment-to-binder ratio. Good results are achieved at pigment-to-binderratios above about 0.175 and at conductive film thicknesses greater thanabout 0.2 mil.

                  TABLE 1                                                         ______________________________________                                        (Resistivity in Ransberg Units)                                                          Pigment-to-Binder Ratios                                           % Elongation 0.23   0.175      0.117                                                                              0.058                                     ______________________________________                                        Test A - Thickness: 0.75 mil                                                  .0           >165   >165       165  83                                        12.5         >165   >165       150  83                                        37.5         >165   >165       160  83                                        43.8         >165   >165       165  83                                        62.5         >165   >165       153  81                                        131          >165   >165       155  81                                        156          >165   >165       155  81                                        Test B - Thickness: 0.35 mil                                                  .0           >165   >165       152  83                                        12.5         >165   >165       152  83                                        37.5         >165   >165       152  83                                        43.8         >165   >165       150  81                                        62.5         >165   >165       151  81                                        131          >165   >165       143  81                                        156          >165   >165       150  81                                        Test C - Thickness: 0.2 mil                                                   0            >165     165      143  83                                        12.5         >165     165      143  83                                        37.5         >165     165      139  83                                        43.8         >165     165      132  82                                        62.5         >165     165      135  81                                        131          >165     151       83  81                                        156          >165     151       80  81                                        Test D - Thickness: 0.1 mil                                                   0              165    149       83  83                                        12.5           165    155       83  83                                        37.5           165    145       83  83                                        43.8           165    140       81  82                                        62.5           165    145       80  81                                        131            147     85       80  81                                        156            139     80       80  81                                        ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        (Resistivity in K-Ohms/Sq. Units)                                                        Pigment-to-Binder Ratios                                           % Elongation .23    0.175      0.117                                                                              0.058                                     ______________________________________                                        Test A - Thickness: 0.75 mil                                                  0            .5     11           500                                                                              >500                                      12.5         .4      6         >500 >500                                      37.5         .45    10         >500 >500                                      43.8         .9      9           400                                                                              >500                                      62.5         .6     11         >500 >500                                      131          1.4    10         >500 >500                                      156          1.2    23           300                                                                              >500                                      Test B - Thickness: 0.35 mil                                                  0            1.8     8         >500 >500                                      12.5         1      30         >500 >500                                      37.5         1.3    29         >500 >500                                      43.8         2.5    90         >500 >500                                      62.5         2      55         >500 >500                                      131          6      76         >500 >500                                      156          12     55         >500 >500                                      Test C - Thickness: 0.2 mil                                                   .0           11.5   200        >500 >500                                      12.5         12     90         >500 >500                                      37.5         25     110        >500 >500                                      43.8         36     300        >500 >500                                      62.5         28     180        >500 >500                                      131          70     400        >500 >500                                      156          80     500        >500 >500                                      Test D - Thickness: 0.1 mil                                                   0            50     >500       >500 >500                                      12.5         90     >500       >500 >500                                      37.5         190    >500       >500 >500                                      43.8         160    >500       >500 >500                                      62.5         250    >500       >500 >500                                      131          500    >500       >500 >500                                      156          500    >500       >500 >500                                      ______________________________________                                    

EXAMPLE 17

In this example the process was modified to test adherence of theconductive coat to a TPO panel. The TPO consisted of ethylene propylenerubber dispersed within polypropylene. The conductive coating in thepolyester resin system from Example 1 was used to make the TPO sheetconductive by use of an understamp made by first casting a tie coat ofDuPont's acrylic 68080 onto a silicone coated release liner from HoechstDiafoil. The acrylic tie coat was applied at a dry film thickness of 0.3mil. A water-based clear coat of a chlorinated polyolefin (CPO) fromAline, A1-112, was cast on the tie coat and dried to a film thickness of0.3 mil. This construction was laminated to a 20 mil thick panel of theTPO. The conductive laminate from Example 1 was then laminated to thisconstruction to produce the following construction:

0.8 mil conductive polyester

0.3 mil acrylic tie coat

0.3 mil chlorinated polyolefin

20 mil TPO This laminate was then vacuum formed over the mold of Example16 and resistivity measurements were taken in Ransberg units andK-ohms/sq. as follows:

    ______________________________________                                        % Elongation   Ransberg K-ohms/sg.                                            ______________________________________                                        0              >165     0.11                                                  12.5           >165     0.11                                                  37.5           >165     0.11                                                  43.5           >165     0.11                                                  62.5           >165     0.20                                                  131            >165     0.18                                                  156            >165     0.20                                                  ______________________________________                                    

The conclusion is that good adhesion of the conductive film can beachieved for a TPO panel when the tie coat is cast separately as anunderstamp, rather than casting it directly on the conductive coat, andby use of the CPO to enhance adhesion. Casting the tie coat separately,followed by laminating avoids solvent attack of the conductive coatwhich may occur if the tie coat is cast directly onto the conductivecoat. The result is that the conductive coat retains good resistivitylevels through a wide range of elongations that simulate threedimensional shaping of the finished panel.

EXAMPLE 18

An acrylic-imide copolymer from Rohm & Haas was used in this example tomanufacture a conductive laminate which can be used in an SMC process.The acrylic was HT-510, an amorphous acrylic-imide copolymer having aT_(g) (glass transition temperature) of 149° C. (The glass transitiontemperature of a plastic is the temperature at which the plastictransitions from a brittle to a rubbery state.) Most acrylics have aT_(g) of 105° C. or lower. The SMC process uses mold temperaturesgreater than about 135° C. This processing temperature melts anddestroys any films made from such acrylics. The conductive film madeusing the HT-510 acrylic-imide appears to survive the SMC process.

The HT-510 was dissolved in methyl ethyl ketone and the XC-72 carbonblack using 1/8 shot, with the following formula:

    ______________________________________                                        Ingredient        Parts                                                       ______________________________________                                        Methyl Ethyl Ketone                                                                             300                                                         HT-510 Acrylic-imide                                                                            100                                                         XC-72 Carbon Black                                                                              23.3                                                        ______________________________________                                    

This conductive primer was then coated onto a matte polyester carrierand dried to a dry film thickness of 0.6 mil. An adhesive tie coat ofIrostic 160/38 from Iromer Chemie was dissolved in methyl ethyl ketone,with the following formula:

    ______________________________________                                        Ingredient        Parts                                                       ______________________________________                                        Methyl Ethyl Ketone                                                                             300                                                         Irostic 16D/38    100                                                         ______________________________________                                    

The tie coat was then coated onto the conductive laminate to a dry filmthickness of 0.1 mil. This construction was heat laminated to a 20 milthick polyarylate sheet to produce the following construction:

    ______________________________________                                               0.6 Mil Conductive Acrylic-imide Coat                                         0.1 Mil Irostic 160/38 Size Coat                                               20 Mil Polyarylate Sheet                                              ______________________________________                                    

Resistivity readings taken in both Ransberg and K-ohms/sq. measuredgreater than 165 Ransberg units, and 1.0 K-ohms/sq.

This example shows a conductive film can be used in an SMC process andmaintained in a coherent state at the higher SMC processing temperatures(above about 149° C.). For material used in an SMC bonding process, itis preferred to use a conductive film and a backing sheet with a T_(g)of at least about 145° C., and more preferably, a T_(g) greater than thetemperature of the sheet molding process.

The polyarylate backing sheet described herein is one example of asuitable backing sheet; other polyarylate backing sheets which can beused are similar to those described in U.S. Pat. Nos. 4,959,189 and5,001,000, incorporated herein by reference.

What is claimed is:
 1. A plastic body panel having a primed outersurface adapted for application of an electrostatically spray paintedpaint coat, the body panel comprising:a thermoformable semi-rigidpolymeric face sheet made of a thermoplastically formable polymericmaterial which has been thermoformed into a three-dimensionallycontoured shape, and an electrically conductive thermoformable polymericprimer coat comprising a dry paint transfer film bonded to an exteriorcontoured surface region of the thermoformed polymeric face sheet,the/conductive dry paint transfer film comprising a thermoplasticallyformable polymeric material containing a dispersed conductive materialproviding electrical conductivity to an exposed surface of the film, theconductive dry paint transfer film having regions thereof which havebeen subjected to elongation in forming the contoured face sheet, theconductive dry paint transfer film having a retained Ransbergresistivity value of at least about 110 units for providing anelectrostatically sprayable surface resistivity to the exposed contouredouter surface of the sheet.
 2. The panel according to claim 1 in whichthe outer surface of the primer coat has a transferred microroughness.3. The panel according to claim 1 in which the conductive primer coatcomprises a polymer resin having a uniformly dispersed particulateconductive filler, the resin being selected from the group consisting ofpolyester, acrylic, polyarylate, urethane and polyetherimide resins. 4.The panel according to claim 3 in which the conductive filler comprisescarbon black.
 5. The panel according to claim 1 in which the panelfurther includes a size coat on a surface of the face sheet oppositefrom the conductive film, and a molded polymeric substrate panel bondedto the thermoformed face sheet via adhesive bonding to the size coat. 6.The panel according to claim 1 in which the conductive primer coatcomprises a thermoplastic or lightly cross-linked thermoset resin havingno more than about ten parts cross-linking resin per 100 partsthermoplastic resin.
 7. The panel according to claim 1 in which theconductive primer coat comprises a thermoset resin and in which thesheet to which it is bonded is a thermoset molding material.
 8. Thepanel according to claim 1 in which the conductive primer has areflectivity greater than about 70% to provide an EMI/RF shielded panel.9. An exterior automotive plastic body panel having a primed outersurface adapted for application of an electrostatically spray paintedexterior automotive paint coat, comprising:a thermoformable semi-rigidpolymeric face sheet made of a thermoplastically formable polymericmaterial which has been thermoformed into a three-dimensionallycontoured shape, an electrically conductive thermoformable polymericprimer coat paint transfer film to an contoured surface region of thethermoformed polymeric face sheet, the conductive dry paint transferfilm comprising a thermoplastically formable polymeric materialcontaining a dispersed conductive material providing electricalconductivity to an outer surface of the film, the conductive dry painttransfer film having regions thereof which have been subjected toelongation in forming the contoured face sheet, the outer surface of theconductive dry paint transfer film having a retained Ransbergresistivity value of at least about 110 units for providing anelectrostatically sprayable surface resistivity to the contoured outersurface of the sheet, a molded polymeric substrate panel bonded to thethermoformed face sheet, and an exterior automotive quality paint coatwith a Class "A" finish applied to the outer surface of the primer coat.10. The panel according to claim 9 in which the outer surface of theprimer coat has a transferred microroughness.
 11. The panel according toclaim 9 in which the conductive primer coat comprises a polymer resinhaving a uniformly dispersed particulate conductive filler, the resinbeing selected from the group consisting of polyester, acrylic,polyarylate, urethane and polyetherimide resins.
 12. The panel accordingto claim 9 in which the conductive filler comprises carbon black. 13.The panel according to claim 9 in which the conductive primer coatcomprises a thermoplastic or lightly cross-linked thermoset resin.
 14. Ashaped plastic automotive body part having a primed outer surfaceadapted for application of an electrostatically spray painted paintcoat, the body part comprising:a semi-rigid thermoformable polymericface sheet made of a thermoplastically formable polymeric material whichhas been thermoformed into a three-dimensionally contoured shape, anelectrically conductive thermoformable polymeric primer coat comprisinga dry paint transfer film bonded to an exterior contoured surface regionof the thermoformed polymeric sheet, the conductive dry paint transferfilm comprising a thermoplastically formable polymeric materialcontaining a dispersed conductive material providing electricalconductivity to an outer surface of the conductive film, the conductivedry paint transfer film having regions thereof which have been subjectedto elongation in forming the contoured face sheet, the conductive drypaint transfer film having a retained Ransberg resistivity value of atleast about 110 units for providing an electrostatically sprayablesurface resistivity to the contoured outer surface of the sheet, and anexterior automotive quality paint coat with a Class "A" finish appliedto the outer surface of the conductive film.
 15. A shaped automotivebody part according to claim 14 in which the conductive primer coatcomprises a thermoplastic or lightly cross-linked thermoset resin havingno more than about ten parts cross-linking resin per 100 partsthermoplastic resin.
 16. A plastic body panel having a primed outersurface adapted for application of an electrostatically spray paintedpaint coat, the body panel comprising:a semi-rigid thermoformablepolymeric face sheet made from thermoplastically formable polymericmaterial which has been thermoformed into a three-dimensionallycontoured shape, the face sheet having a thickness in the range fromabout 10 to about 200 mils, an electrically conductive thermoformablepolymeric primer coat comprising a dry paint transfer film bonded to anexterior contoured surface region of the thermoformed polymeric sheet,the polymeric material containing a dispersed conductive materialproviding electrical conductivity to an exposed outer surface of thefilm, the outer surface of the conductive dry paint transfer film havinga microroughness transferred to it from replicating contact with acarrier on which the dry paint transfer film is formed, the conductivedry paint transfer film having regions thereof which have been subjectedto elongation in forming the contoured face sheet, the conductive filmhaving a retained Ransberg resistivity value of at least about 110 unitsfor providing an electrostatically sprayable surface resistivity to thecontoured outer surface of the sheet.
 17. A body panel according toclaim 16 in which the conductive primer coat comprises a thermoplasticor lightly cross-linked thermoset resin having no more than about tenparts cross-linking resin per 100 parts thermoplastic resin.